So, I am looking at our future bats(Almora, Soler, Baez, Bryant) and it seems like we have a lot of right handed batters, along with Castro and Wellington Castillo. The only "core" player we really have that is a left handed bat is Rizzo.
Obviously some of the prospects may not work out, but thats 6 right handed bats in 8 spots. Maybe you can count Alcantra(Switch hitter)/Watkins at 2nd, with Baez at 3rd and Bryant in LF.
If he doesn't demand a lot of money, how would Brian McCann fit in with the Cubs? He will only be 30 years old at the start of next season and could add some thump to the lineup. Keep Castillo as a very nice backup and work him in a few days, keeping McCann fresh since he has had some injuries in the past. Get him signed to a 4 year deal or so, he could contribute to the team when we should be ready to compete, as well as a good catcher for young pitchers.